Degree Name

Doctor of Philosophy


School of Electrical, Computer and Telecommunications Engineering


Development of a device capable of producing a high power atmospheric pressure plasma beam has been one of the goals of researchers since the development of the magnetron. Until now, progress has been hampered for a variety of technical reasons not the least being materials limitations and the unavailability of suitable microwave generators. The work set forth in this dissertation describes the development of an efficient, atmospheric pressure, plasma beam applicator capable of sustained operation at powers in excess of 5 kW. Sustained operation at such high powers is accomplished through innovative cooling techniques. The operating parameters necessary to produce a stable plasma beam are elaborated upon, as are the physical properties of the plasma. Properties such as beam temperature, length and pressure are characterised as a function of the operating parameters of the system. Beam temperatures are determined using laser scattering techniques from which 2D temperature profiles of the beam are reconstructed.

The voltage standing wave ratio and complex impedance of the plasma are determined as a function of microwave power, discharge gas flow rate and state of tuning of the applicator for both cooled and non-cooled versions of the waveguide applicator. An electric circuit model of the plasma/applicator system is then derived from these measurements. Temperatures and impedances are compared to those reported in the literature for similarly generated microwave plasmas.

Application of a microwave plasma beam to welding and joining applications is totally absent from the literature. In this thesis, autogenous butt welding of sheet steel detailed and examination of the weld strength and weld microstructure as a function of microwave power, discharge gas flow rate and travel speed performed. Results indicate that welds performed using a microwave plasma beam are comparable in appearance and quality to those generated using gas tungsten arc welding techniques.